Triphosgene is chemically known as bis(trichloromethyl)carbonate, with the appearance of white crystals, so it is also known as solid phosgene. Molecular weight 296.75, melting point 79-83 ℃, boiling point 203-206 ℃, density 1.78g/cm3. can be dissolved in benzene, toluene, ether, tetrahydrofuran, cyclohexane, chloroform and other organic solvents. Under normal conditions, triphosgene is chemically stable, without significant toxicity, and can successfully replace phosgene to achieve the goal of organic synthesis of many photogasification reactions. Compared with other reaction reagents, triphosgene also has more advantages, such as the role of the reactants with the more completely close to the equivalent ratio; the reaction conditions are milder; the purity of the synthesized product and yield significantly improved. Therefore, triphosgene has been increasingly widely used in chemical production. However, the gas will be slightly decomposed to produce phosgene when the temperature is higher than 130℃. After absorbing moisture, it will start to decompose and produce phosgene at 90℃. Some impurities (such as organic amines) have a catalytic effect on the decomposition of phosgene, which will cause the rapid decomposition of phosgene at lower temperatures. At high temperatures, it is cracked into phosgene, carbon dioxide and carbon tetrachloride. The main hazard in the production, use and storage of triphosgene is poisoning.
January 6, 2011, Anhui Province, Suzhou City, Wanbei Pharmaceutical Plant pilot plant occurred in the decomposition of the gas leakage accident, the accident caused 2 deaths, 71 people were poisoned. In view of the great danger that may arise in the process of production and use of three light gas, I organized experts to the cause of the accident was seriously analyzed and discussed, on the prevention of three light gas production and use of decomposition and leakage accidents, put forward the following safety countermeasures and recommendations.
I, process safety
1, strictly in accordance with the equivalent ratio of feeding, prohibit the three light gas overfeeding. The solvent and material participating in the reaction should control the moisture content, and the equipment piping system should be dried.
2, the operation of the reaction temperature must be strictly controlled, prohibit the operator to shorten the reaction time and increase the reaction temperature, to avoid the decomposition of a large number of phosgene into phosgene.
3, the end of the reaction should be detected after the exhaustion of the three light gas, such as not exhausted can be used to increase the reaction time or a small amount of reaction materials to be added to the exhaustion of the three light gas, to avoid the material containing three light gas to the next process.
4, after the end of the reaction can be appropriate to raise the temperature of the material and nitrogen to drive the possible existence of the gas into the gas decomposition and destruction of the device.
5, the production of three gas device should strictly control the flow of chlorine, the reaction temperature and the amount of peroxide catalyst, to prevent the free radical chain reaction out of control leading to the decomposition of three gas generated in the device, the chlorination reaction must be used to automatically control.
6, involving three light gas reaction unit of solvent recovery, such as solvents may exist in organic amines, try not to apply. If you consider applying, you must control the organic amine content in the solvent, and implement strict testing.
7, research to find other safer, more efficient process route instead of three light gas process route, essentially improve process safety.
Two, equipment safety
1, in order to ensure that the gas may not come into contact with high temperature conditions, all the reaction equipment containing the gas (including containers containing the gas) shall not be connected to the jacket with steam heating pipeline, such as the need for heating can be indirectly heated with lukewarm water. All pipes connected to the jacket of the reactor must be inspected and confirmed to eliminate all possibilities of escaping steam. With water-cooled jacketed kettle, should regularly check the kettle wall corrosion and strength, to prevent perforation of water into the reaction.
2, the production or use of three phosgene reaction device must be attached to the tail gas (may contain phosgene) decomposition and destruction device, reaction kettle exhaust gas and reaction chamber exhaust indoor air must be sent to the phosgene decomposition and destruction device. The phosgene decomposition and destruction device includes a lye decomposition and destruction tower, a lye storage tank and a lye circulation pump. The alkaline water can use 10% sodium hydroxide solution. The lye water sent into the gas decomposition destruction tower shall not be interrupted in the reaction, and the backup pump shall be automatically turned on and an alarm shall be issued at the same time when the lye water circulation pump fails. The whole phosgene decomposition destructive device must also have a backup system, when an unexpected situation can open the backup processing system. The phosgene decomposition destructive device can also use SN-7501 catalyst loading phosgene decomposition destructive tower, the effect will be better.
3, the production or use of three light gas all the equipment must be centrally arranged in an isolated closed production workshop, the production workshop should not be less than two entrances per floor area less than or equal to 100m2; each floor area of more than 100m2 should not be less than three entrances; two or more floors above the plant each floor must be a staircase leading directly to the outdoors. Under normal circumstances, the entrance and exit doors must be kept closed.
4, the production or use of gas production workshop should be equipped with exhaust devices, so that the production site to maintain a slightly negative pressure, the discharged air should be sent by pipeline to the tail gas (phosgene) decomposition and destruction of the tower, it is strictly prohibited to directly exhaust; at the same time, the exhaust device should be located in the downwind direction of the plant. When the material containing three phosgene leakage or phosgene leakage occurs in the production place, dilute ammonia or dilute alkaline water can be used to spray treatment, so the production place should be installed with dilute ammonia or dilute alkaline water emergency spray facilities. It is also possible to use ammonia or water vapor into the production site. The use of ammonia should pay attention to prevent ammonia poisoning.
5, the production or use of three light gas reaction equipment must be kept closed, containing three light gas material rotation equipment should be used to seal the reliable performance of the device. Reaction equipment should not be run under pressure, should not be set up glass sight glass, conveying liquid pipeline containing SFG should not be set up glass sight glass. Reaction equipment, storage tanks, piping, valves, gaskets and other materials in contact with the three light gas-containing materials should be selected appropriate corrosion-resistant materials.
6, the reaction device should ensure adequate freezing (cooling) conditions with the participation of gas, gas dissolution kettle, gas reaction kettle as well as the drop of gas and high level tank containers and other equipment should take good thermal insulation measures.
7, in order to prevent accidents caused by power failure, the production or use of three light gas reaction equipment, control devices, tail gas decomposition tower and other related equipment, as well as frozen brine transfer pumps should be provided with standby emergency power.
Three, self-control safety
1, the use of three light gas production sites should be set up to isolate the operating room, the operator and the production site to implement closed isolation.
2, the temperature of the reaction process should be containing three gas material and material liquid drop valve (or chlorine flow) to implement chain cut-off control and over-temperature alarm.
3, in the production or use of three gas and exhaust gas treatment device in the place of exhaust pipe installation for the gas of the toxic gas detection and alarm devices. The setting value of the toxic gas detection alarm in the production place should be the exposure limit of phosgene in the production place (MAC=0.5mg/m3) as stipulated in the national occupational health standard. The set value of the toxic gas detection alarm of the exhaust vent should be the phosgene emission standard (3mg/m3) stipulated by the national environmental protection standard.
4, three phosgene operation room of the toxic gas detection detection alarm device should have chain processing function. When the exhaust gas treatment device of the exhaust pipe mouth phosgene content exceeds the standard, should immediately start the backup tail gas treatment device; when the three phosgene operating room phosgene content exceeds the standard should immediately start the indoor dilute alkaline water (or ammonia) spray treatment device.
Four, storage safety
1, three light gas in the warehouse must be set up in a single room separate storage, should not be stored with other chemicals. Three light gas storage room and adjacent rooms must be separated by firewalls, no doors, windows, holes, holes, to prevent the occurrence of various types of fire accidents.
2, three gas storage room must be set up toxic gas (phosgene) detector alarm, once produced phosgene that chain start dilute alkaline water (ammonia) emergency spray device to eliminate the production of phosgene.
3, three phosgene storage room must be set up early fire detection and alarm devices and chain bubble bath fire extinguishing device, in the high temperature water is prohibited to extinguish fires.
4, three gas storage should be controlled in the minimum limit, the production of three gas units should be sold to reduce inventory, the use of three gas units should be carried out less storage, the principle of diligence into.
V. Emergency safety
1, the production and storage of three light gas production and storage sites posted danger signs, prohibit unrelated personnel close.
2, the three light gas and phosgene physical and chemical properties, process and technical procedures, safe operation procedures for training and education of employees before starting work, the quality of employees in accordance with the requirements of the light gasification production equipment.
3, the preparation of three light gas production and use of abnormalities in the emergency response plan, and organize experts to demonstrate, conduct drills.
4, for employees equipped with labor protection equipment adapted to phosgene anti-poisoning, the production site is equipped with sufficient first-aid medicines for phosgene poisoning.
5, in advance, the nearest contact counterpart emergency hospitals, first aid methods of phosgene poisoning will be communicated with medical personnel in advance, to prevent the occurrence of rescue errors.
6, the production workshop should be equipped with emergency shower device, prohibit eating in the production place and shall not store food.
7, the factory should be set up wind vane, when a toxic gas leakage evacuees should be moved upwind. The location and height of the wind vane should be set to ensure that the unit workers and nearby 500m range of people can easily see.
8, although the three light gas does not belong to the "List of Dangerous Chemicals" 2002 version of the scope, but in the transport should be entrusted to the professional hazardous chemicals transport enterprises and take the necessary safety measures.